/*
* Copyright (C) 2014 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <keymaster/keymaster_enforcement.h>
#include <assert.h>
#include <limits.h>
#include <string.h>
#include <openssl/evp.h>
#include <hardware/hw_auth_token.h>
#include <keymaster/android_keymaster_utils.h>
#include <keymaster/logger.h>
#include "List.h"
using android::List;
namespace keymaster {
class AccessTimeMap {
public:
AccessTimeMap(uint32_t max_size) : max_size_(max_size) {}
/* If the key is found, returns true and fills \p last_access_time. If not found returns
* false. */
bool LastKeyAccessTime(km_id_t keyid, uint32_t* last_access_time) const;
/* Updates the last key access time with the currentTime parameter. Adds the key if
* needed, returning false if key cannot be added because list is full. */
bool UpdateKeyAccessTime(km_id_t keyid, uint32_t current_time, uint32_t timeout);
private:
struct AccessTime {
km_id_t keyid;
uint32_t access_time;
uint32_t timeout;
};
android::List<AccessTime> last_access_list_;
const uint32_t max_size_;
};
class AccessCountMap {
public:
AccessCountMap(uint32_t max_size) : max_size_(max_size) {}
/* If the key is found, returns true and fills \p count. If not found returns
* false. */
bool KeyAccessCount(km_id_t keyid, uint32_t* count) const;
/* Increments key access count, adding an entry if the key has never been used. Returns
* false if the list has reached maximum size. */
bool IncrementKeyAccessCount(km_id_t keyid);
private:
struct AccessCount {
km_id_t keyid;
uint64_t access_count;
};
android::List<AccessCount> access_count_list_;
const uint32_t max_size_;
};
bool is_public_key_algorithm(const AuthorizationSet& auth_set) {
keymaster_algorithm_t algorithm;
return auth_set.GetTagValue(TAG_ALGORITHM, &algorithm) &&
(algorithm == KM_ALGORITHM_RSA || algorithm == KM_ALGORITHM_EC);
}
static keymaster_error_t authorized_purpose(const keymaster_purpose_t purpose,
const AuthorizationSet& auth_set) {
switch (purpose) {
case KM_PURPOSE_VERIFY:
case KM_PURPOSE_ENCRYPT:
case KM_PURPOSE_SIGN:
case KM_PURPOSE_DECRYPT:
if (auth_set.Contains(TAG_PURPOSE, purpose))
return KM_ERROR_OK;
return KM_ERROR_INCOMPATIBLE_PURPOSE;
default:
return KM_ERROR_UNSUPPORTED_PURPOSE;
}
}
inline bool is_origination_purpose(keymaster_purpose_t purpose) {
return purpose == KM_PURPOSE_ENCRYPT || purpose == KM_PURPOSE_SIGN;
}
inline bool is_usage_purpose(keymaster_purpose_t purpose) {
return purpose == KM_PURPOSE_DECRYPT || purpose == KM_PURPOSE_VERIFY;
}
KeymasterEnforcement::KeymasterEnforcement(uint32_t max_access_time_map_size,
uint32_t max_access_count_map_size)
: access_time_map_(new (std::nothrow) AccessTimeMap(max_access_time_map_size)),
access_count_map_(new (std::nothrow) AccessCountMap(max_access_count_map_size)) {}
KeymasterEnforcement::~KeymasterEnforcement() {
delete access_time_map_;
delete access_count_map_;
}
keymaster_error_t KeymasterEnforcement::AuthorizeOperation(const keymaster_purpose_t purpose,
const km_id_t keyid,
const AuthorizationSet& auth_set,
const AuthorizationSet& operation_params,
keymaster_operation_handle_t op_handle,
bool is_begin_operation) {
if (is_public_key_algorithm(auth_set)) {
switch (purpose) {
case KM_PURPOSE_ENCRYPT:
case KM_PURPOSE_VERIFY:
/* Public key operations are always authorized. */
return KM_ERROR_OK;
case KM_PURPOSE_DECRYPT:
case KM_PURPOSE_SIGN:
case KM_PURPOSE_DERIVE_KEY:
break;
};
};
if (is_begin_operation)
return AuthorizeBegin(purpose, keyid, auth_set, operation_params);
else
return AuthorizeUpdateOrFinish(auth_set, operation_params, op_handle);
}
// For update and finish the only thing to check is user authentication, and then only if it's not
// timeout-based.
keymaster_error_t
KeymasterEnforcement::AuthorizeUpdateOrFinish(const AuthorizationSet& auth_set,
const AuthorizationSet& operation_params,
keymaster_operation_handle_t op_handle) {
int auth_type_index = -1;
for (size_t pos = 0; pos < auth_set.size(); ++pos) {
switch (auth_set[pos].tag) {
case KM_TAG_NO_AUTH_REQUIRED:
case KM_TAG_AUTH_TIMEOUT:
// If no auth is required or if auth is timeout-based, we have nothing to check.
return KM_ERROR_OK;
case KM_TAG_USER_AUTH_TYPE:
auth_type_index = pos;
break;
default:
break;
}
}
// Note that at this point we should be able to assume that authentication is required, because
// authentication is required if KM_TAG_NO_AUTH_REQUIRED is absent. However, there are legacy
// keys which have no authentication-related tags, so we assume that absence is equivalent to
// presence of KM_TAG_NO_AUTH_REQUIRED.
//
// So, if we found KM_TAG_USER_AUTH_TYPE or if we find KM_TAG_USER_SECURE_ID then authentication
// is required. If we find neither, then we assume authentication is not required and return
// success.
bool authentication_required = (auth_type_index != -1);
for (auto& param : auth_set) {
if (param.tag == KM_TAG_USER_SECURE_ID) {
authentication_required = true;
int auth_timeout_index = -1;
if (AuthTokenMatches(auth_set, operation_params, param.long_integer, auth_type_index,
auth_timeout_index, op_handle, false /* is_begin_operation */))
return KM_ERROR_OK;
}
}
if (authentication_required)
return KM_ERROR_KEY_USER_NOT_AUTHENTICATED;
return KM_ERROR_OK;
}
keymaster_error_t KeymasterEnforcement::AuthorizeBegin(const keymaster_purpose_t purpose,
const km_id_t keyid,
const AuthorizationSet& auth_set,
const AuthorizationSet& operation_params) {
// Find some entries that may be needed to handle KM_TAG_USER_SECURE_ID
int auth_timeout_index = -1;
int auth_type_index = -1;
int no_auth_required_index = -1;
for (size_t pos = 0; pos < auth_set.size(); ++pos) {
switch (auth_set[pos].tag) {
case KM_TAG_AUTH_TIMEOUT:
auth_timeout_index = pos;
break;
case KM_TAG_USER_AUTH_TYPE:
auth_type_index = pos;
break;
case KM_TAG_NO_AUTH_REQUIRED:
no_auth_required_index = pos;
break;
default:
break;
}
}
keymaster_error_t error = authorized_purpose(purpose, auth_set);
if (error != KM_ERROR_OK)
return error;
// If successful, and if key has a min time between ops, this will be set to the time limit
uint32_t min_ops_timeout = UINT32_MAX;
bool update_access_count = false;
bool caller_nonce_authorized_by_key = false;
bool authentication_required = false;
bool auth_token_matched = false;
for (auto& param : auth_set) {
// KM_TAG_PADDING_OLD and KM_TAG_DIGEST_OLD aren't actually members of the enum, so we can't
// switch on them. There's nothing to validate for them, though, so just ignore them.
if (param.tag == KM_TAG_PADDING_OLD || param.tag == KM_TAG_DIGEST_OLD)
continue;
switch (param.tag) {
case KM_TAG_ACTIVE_DATETIME:
if (!activation_date_valid(param.date_time))
return KM_ERROR_KEY_NOT_YET_VALID;
break;
case KM_TAG_ORIGINATION_EXPIRE_DATETIME:
if (is_origination_purpose(purpose) && expiration_date_passed(param.date_time))
return KM_ERROR_KEY_EXPIRED;
break;
case KM_TAG_USAGE_EXPIRE_DATETIME:
if (is_usage_purpose(purpose) && expiration_date_passed(param.date_time))
return KM_ERROR_KEY_EXPIRED;
break;
case KM_TAG_MIN_SECONDS_BETWEEN_OPS:
min_ops_timeout = param.integer;
if (!MinTimeBetweenOpsPassed(min_ops_timeout, keyid))
return KM_ERROR_KEY_RATE_LIMIT_EXCEEDED;
break;
case KM_TAG_MAX_USES_PER_BOOT:
update_access_count = true;
if (!MaxUsesPerBootNotExceeded(keyid, param.integer))
return KM_ERROR_KEY_MAX_OPS_EXCEEDED;
break;
case KM_TAG_USER_SECURE_ID:
if (no_auth_required_index != -1) {
// Key has both KM_TAG_USER_SECURE_ID and KM_TAG_NO_AUTH_REQUIRED
return KM_ERROR_INVALID_KEY_BLOB;
}
if (auth_timeout_index != -1) {
authentication_required = true;
if (AuthTokenMatches(auth_set, operation_params, param.long_integer,
auth_type_index, auth_timeout_index, 0 /* op_handle */,
true /* is_begin_operation */))
auth_token_matched = true;
}
break;
case KM_TAG_CALLER_NONCE:
caller_nonce_authorized_by_key = true;
break;
/* Tags should never be in key auths. */
case KM_TAG_INVALID:
case KM_TAG_AUTH_TOKEN:
case KM_TAG_ROOT_OF_TRUST:
case KM_TAG_APPLICATION_DATA:
case KM_TAG_ATTESTATION_CHALLENGE:
return KM_ERROR_INVALID_KEY_BLOB;
/* Tags used for cryptographic parameters in keygen. Nothing to enforce. */
case KM_TAG_PURPOSE:
case KM_TAG_ALGORITHM:
case KM_TAG_KEY_SIZE:
case KM_TAG_BLOCK_MODE:
case KM_TAG_DIGEST:
case KM_TAG_MAC_LENGTH:
case KM_TAG_PADDING:
case KM_TAG_NONCE:
case KM_TAG_MIN_MAC_LENGTH:
case KM_TAG_KDF:
case KM_TAG_EC_CURVE:
/* Tags not used for operations. */
case KM_TAG_BLOB_USAGE_REQUIREMENTS:
case KM_TAG_EXPORTABLE:
/* Algorithm specific parameters not used for access control. */
case KM_TAG_RSA_PUBLIC_EXPONENT:
case KM_TAG_ECIES_SINGLE_HASH_MODE:
/* Informational tags. */
case KM_TAG_CREATION_DATETIME:
case KM_TAG_ORIGIN:
case KM_TAG_ROLLBACK_RESISTANT:
/* Tags handled when KM_TAG_USER_SECURE_ID is handled */
case KM_TAG_NO_AUTH_REQUIRED:
case KM_TAG_USER_AUTH_TYPE:
case KM_TAG_AUTH_TIMEOUT:
/* Tag to provide data to operations. */
case KM_TAG_ASSOCIATED_DATA:
/* Tags that are implicitly verified by secure side */
case KM_TAG_ALL_APPLICATIONS:
case KM_TAG_APPLICATION_ID:
case KM_TAG_OS_VERSION:
case KM_TAG_OS_PATCHLEVEL:
/* Ignored pending removal */
case KM_TAG_USER_ID:
case KM_TAG_ALL_USERS:
/* TODO(swillden): Handle these */
case KM_TAG_INCLUDE_UNIQUE_ID:
case KM_TAG_UNIQUE_ID:
case KM_TAG_RESET_SINCE_ID_ROTATION:
case KM_TAG_ALLOW_WHILE_ON_BODY:
break;
case KM_TAG_BOOTLOADER_ONLY:
return KM_ERROR_INVALID_KEY_BLOB;
}
}
if (authentication_required && !auth_token_matched) {
LOG_E("Auth required but no matching auth token found", 0);
return KM_ERROR_KEY_USER_NOT_AUTHENTICATED;
}
if (!caller_nonce_authorized_by_key && is_origination_purpose(purpose) &&
operation_params.find(KM_TAG_NONCE) != -1)
return KM_ERROR_CALLER_NONCE_PROHIBITED;
if (min_ops_timeout != UINT32_MAX) {
if (!access_time_map_) {
LOG_S("Rate-limited keys table not allocated. Rate-limited keys disabled", 0);
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
}
if (!access_time_map_->UpdateKeyAccessTime(keyid, get_current_time(), min_ops_timeout)) {
LOG_E("Rate-limited keys table full. Entries will time out.", 0);
return KM_ERROR_TOO_MANY_OPERATIONS;
}
}
if (update_access_count) {
if (!access_count_map_) {
LOG_S("Usage-count limited keys tabel not allocated. Count-limited keys disabled", 0);
return KM_ERROR_MEMORY_ALLOCATION_FAILED;
}
if (!access_count_map_->IncrementKeyAccessCount(keyid)) {
LOG_E("Usage count-limited keys table full, until reboot.", 0);
return KM_ERROR_TOO_MANY_OPERATIONS;
}
}
return KM_ERROR_OK;
}
class EvpMdCtx {
public:
EvpMdCtx() { EVP_MD_CTX_init(&ctx_); }
~EvpMdCtx() { EVP_MD_CTX_cleanup(&ctx_); }
EVP_MD_CTX* get() { return &ctx_; }
private:
EVP_MD_CTX ctx_;
};
/* static */
bool KeymasterEnforcement::CreateKeyId(const keymaster_key_blob_t& key_blob, km_id_t* keyid) {
EvpMdCtx ctx;
uint8_t hash[EVP_MAX_MD_SIZE];
unsigned int hash_len;
if (EVP_DigestInit_ex(ctx.get(), EVP_sha256(), nullptr /* ENGINE */) &&
EVP_DigestUpdate(ctx.get(), key_blob.key_material, key_blob.key_material_size) &&
EVP_DigestFinal_ex(ctx.get(), hash, &hash_len)) {
assert(hash_len >= sizeof(*keyid));
memcpy(keyid, hash, sizeof(*keyid));
return true;
}
return false;
}
bool KeymasterEnforcement::MinTimeBetweenOpsPassed(uint32_t min_time_between, const km_id_t keyid) {
if (!access_time_map_)
return false;
uint32_t last_access_time;
if (!access_time_map_->LastKeyAccessTime(keyid, &last_access_time))
return true;
return min_time_between <= static_cast<int64_t>(get_current_time()) - last_access_time;
}
bool KeymasterEnforcement::MaxUsesPerBootNotExceeded(const km_id_t keyid, uint32_t max_uses) {
if (!access_count_map_)
return false;
uint32_t key_access_count;
if (!access_count_map_->KeyAccessCount(keyid, &key_access_count))
return true;
return key_access_count < max_uses;
}
bool KeymasterEnforcement::AuthTokenMatches(const AuthorizationSet& auth_set,
const AuthorizationSet& operation_params,
const uint64_t user_secure_id,
const int auth_type_index, const int auth_timeout_index,
const keymaster_operation_handle_t op_handle,
bool is_begin_operation) const {
assert(auth_type_index < static_cast<int>(auth_set.size()));
assert(auth_timeout_index < static_cast<int>(auth_set.size()));
keymaster_blob_t auth_token_blob;
if (!operation_params.GetTagValue(TAG_AUTH_TOKEN, &auth_token_blob)) {
LOG_E("Authentication required, but auth token not provided", 0);
return false;
}
if (auth_token_blob.data_length != sizeof(hw_auth_token_t)) {
LOG_E("Bug: Auth token is the wrong size (%d expected, %d found)", sizeof(hw_auth_token_t),
auth_token_blob.data_length);
return false;
}
hw_auth_token_t auth_token;
memcpy(&auth_token, auth_token_blob.data, sizeof(hw_auth_token_t));
if (auth_token.version != HW_AUTH_TOKEN_VERSION) {
LOG_E("Bug: Auth token is the version %d (or is not an auth token). Expected %d",
auth_token.version, HW_AUTH_TOKEN_VERSION);
return false;
}
if (!ValidateTokenSignature(auth_token)) {
LOG_E("Auth token signature invalid", 0);
return false;
}
if (auth_timeout_index == -1 && op_handle && op_handle != auth_token.challenge) {
LOG_E("Auth token has the challenge %llu, need %llu", auth_token.challenge, op_handle);
return false;
}
if (user_secure_id != auth_token.user_id && user_secure_id != auth_token.authenticator_id) {
LOG_I("Auth token SIDs %llu and %llu do not match key SID %llu", auth_token.user_id,
auth_token.authenticator_id, user_secure_id);
return false;
}
if (auth_type_index < 0 || auth_type_index > static_cast<int>(auth_set.size())) {
LOG_E("Auth required but no auth type found", 0);
return false;
}
assert(auth_set[auth_type_index].tag == KM_TAG_USER_AUTH_TYPE);
if (auth_set[auth_type_index].tag != KM_TAG_USER_AUTH_TYPE)
return false;
uint32_t key_auth_type_mask = auth_set[auth_type_index].integer;
uint32_t token_auth_type = ntoh(auth_token.authenticator_type);
if ((key_auth_type_mask & token_auth_type) == 0) {
LOG_E("Key requires match of auth type mask 0%uo, but token contained 0%uo",
key_auth_type_mask, token_auth_type);
return false;
}
if (auth_timeout_index != -1 && is_begin_operation) {
assert(auth_set[auth_timeout_index].tag == KM_TAG_AUTH_TIMEOUT);
if (auth_set[auth_timeout_index].tag != KM_TAG_AUTH_TIMEOUT)
return false;
if (auth_token_timed_out(auth_token, auth_set[auth_timeout_index].integer)) {
LOG_E("Auth token has timed out", 0);
return false;
}
}
// Survived the whole gauntlet. We have authentage!
return true;
}
bool AccessTimeMap::LastKeyAccessTime(km_id_t keyid, uint32_t* last_access_time) const {
for (auto& entry : last_access_list_)
if (entry.keyid == keyid) {
*last_access_time = entry.access_time;
return true;
}
return false;
}
bool AccessTimeMap::UpdateKeyAccessTime(km_id_t keyid, uint32_t current_time, uint32_t timeout) {
List<AccessTime>::iterator iter;
for (iter = last_access_list_.begin(); iter != last_access_list_.end();) {
if (iter->keyid == keyid) {
iter->access_time = current_time;
return true;
}
// Expire entry if possible.
assert(current_time >= iter->access_time);
if (current_time - iter->access_time >= iter->timeout)
iter = last_access_list_.erase(iter);
else
++iter;
}
if (last_access_list_.size() >= max_size_)
return false;
AccessTime new_entry;
new_entry.keyid = keyid;
new_entry.access_time = current_time;
new_entry.timeout = timeout;
last_access_list_.push_front(new_entry);
return true;
}
bool AccessCountMap::KeyAccessCount(km_id_t keyid, uint32_t* count) const {
for (auto& entry : access_count_list_)
if (entry.keyid == keyid) {
*count = entry.access_count;
return true;
}
return false;
}
bool AccessCountMap::IncrementKeyAccessCount(km_id_t keyid) {
for (auto& entry : access_count_list_)
if (entry.keyid == keyid) {
// Note that the 'if' below will always be true because KM_TAG_MAX_USES_PER_BOOT is a
// uint32_t, and as soon as entry.access_count reaches the specified maximum value
// operation requests will be rejected and access_count won't be incremented any more.
// And, besides, UINT64_MAX is huge. But we ensure that it doesn't wrap anyway, out of
// an abundance of caution.
if (entry.access_count < UINT64_MAX)
++entry.access_count;
return true;
}
if (access_count_list_.size() >= max_size_)
return false;
AccessCount new_entry;
new_entry.keyid = keyid;
new_entry.access_count = 1;
access_count_list_.push_front(new_entry);
return true;
}
}; /* namespace keymaster */